1. Field of the Invention
This invention relates to a semiconductor device, its manufacturing method and an electrodeposition frame, and more particularly to a leadless surface-mounted resin-sealed semiconductor device, its manufacturing method and an electrodeposition frame on which a semiconductor device is mounted.
2. Description of the Related Art
FIG. 8 is a sectional view showing a conventional semiconductor device which is a leadless surface-mounted resin-sealed semiconductor device.
As seen from FIG. 8, metallic layers 31 and 32 are formed on the front surface of a glass epoxy substrate (or ceramic substrate), whereas an electrode metallic layer 5a is formed on the rear surface thereof so as to correspond to the metallic layer 32. The metallic layer 32 and the electrode metallic layer 5a are electrically conceited to each other via through-holes 6.
A semiconductor element 2 is bonded onto the metallic layer 31 of the glass epoxy substrate 1: Electrode pads 2a of the semiconductor element 2 and the metallic layer 32 are electrically connected by wirings 4. The semiconductor element with the wirings is resin-sealed by epoxy resin 7.
In the conventional leadless surface-mounted type semiconductor device, as shown in FIG. 8, a large number of through-holes 6 are formed on the glass epoxy substrate 1, a large number of metallic layers 31 are formed on the glass epoxy substrate 1, and the semiconductor element 2 is bonded to each of the metallic layers 31. The electrode pads 2a of the semiconductor element are connected to the metallic layers 32 via the wirings 4.
In a process of manufacturing a semiconductor device, semiconductor elements which are located in several hundreds on a single glass epoxy substrate are wire-bonded and resin-sealed.
Therefore, in the semiconductor device having a such a structure, the number of through-holes 6 is several times as large as that of the semiconductor elements 2 so that the number of man-hours for forming the through-holes cannot be disregarded. This has been a cause of increasing the production cost of such a semiconductor device.
Further, in the leadless surface-mounted type semiconductor device, in order to form a through-hole in a gap between the adjacent semiconductor elements, an area where the through-hole is to be formed must be prepared in the gap. Therefore, the actual number of the semiconductor elements which can be mounted in the single glass epoxy substrate is limited. This also has been a cause of increasing the production cost.
Furthermore, in the conventional leadless surface-mounted semiconductor device, the semiconductor devices mounted on the glass epoxy substrate are resin-sealed. Therefore, heat generated when the semiconductor element operates is not dissipated but stored in the glass epoxy substrate. Namely, the conventional leadless surface-mounted semiconductor device has poor heat dissipation.
This invention has been accomplished in order to obviate the inconveniences described above.
A first object of this invention is to provide a leadless surface-mounted semiconductor device which can be manufactured at low cost and provides improved heat dissipation.
A second object of this invention is to provide a method of manufacturing such a semiconductor device.
In order to attain the first object, semiconductor device comprising:
a semiconductor element bonded on a first metallic layer;
a wire for electrically connecting an electrode pad of the semiconductor element to a second metallic layer; and
a resin package for sealing the semiconductor element,
wherein rear surfaces of the first metallic layer and the second metallic layer are flush with a bottom of the resin package.
This configuration provides a leadless semiconductor device in which the semiconductor element sealed within the resin package is mounted on the metallic film exposed from the bottom of the resin package and the metallic layer for external extension is exposed from the bottom of the resin package. In this configuration, a glass epoxy substrate or a ceramic substrate is not employed. Therefore, the semiconductor device can be made low in height so that good heat dissipation from the semiconductor element can be given. Since the above metallic layers are thin films, the leadless semiconductor device with good conductivity can be provided as compared with the semiconductor device using leads.
Since the semiconductor device does not require an expensive substrate, it can be manufactured at relatively low cost. In addition, since the metallic layers and the resin package are flush with each other on the rear surface of the semiconductor substrate, when the semiconductor device is mounted on a circuit board, it can be brought into intimate contact with the circuit board. Further, heat generated from the semiconductor elements can be easily dissipated through the circuit board. A very thin flat electrode metallic layer may be deposited on the rear surface of the metallic layer for external extension as occasion demands.
Preferably, the first metallic layer on which the semiconductor element is placed has a larger area than that of a bottom surface of the semiconductor element.
This configuration provides a sufficient creepage distance from the surface of the resin package to the semiconductor element, thus improving humidity resistance of the semiconductor element.
Preferably, the first metallic layer is thicker than the second metallic layer, and the first metallic layer has a smaller area than a bottom area of the semiconductor element.
In this configuration, since the metallic layer on which the semiconductor element is placed is thicker, a sufficient creepage distance from the bottom of the resin package to the semiconductor element can be given so that the semiconductor device is given improved humidity resistance, and the semiconductor element having a relatively large size can be resin sealed.
Further, since the metallic layer on which semiconductor element is placed is made thicker, the semiconductor element can be arranged centrally within the resin package. For this reason, even when the semiconductor device suffers from thermal stress, the resin package is difficult to rupture.
Preferably, the second metallic layer for external extension is individually exposed from a bottom of the resin package.
In this configuration, the second metallic layer can take any optional shape. It is needless to say that the second metallic layer is made integral.
In accordance with another aspect of this invention, there is provided a method of manufacturing a semiconductor device comprising the steps of:
forming an electrodeposition frame on a flexible flat metallic substrate, the electrodeposition frame with first metallic layers and second metallic layers for external extension being patterned;
contiguously mounting a plurality of semiconductor elements each with electrode pads thereon, on the first metallic layers, respectively;
wire-bonding the electrode pads to the second metallic layers which are located between the semiconductor elements;
resin-sealing the semiconductor elements mounted on the electrodeposition frame;
removing the metallic substrate to provide a resin sealing body; and
cutting the resin sealing body into individual semiconductor devices with the air of cutting marks formed the first and second metallic layers.
This provides a method of manufacturing a semiconductor device using a flexible flat metallic substrate but not a substrate similar to the glass epoxy resin. By removing the flexible flat metallic substrate of the electrodeposition frame, the resin sealing body with a large number of semiconductor elements resin-sealed can be formed. Since the metallic substrate is flexible, when the metallic substrate is removed from the resin sealing body, the resin sealing body is difficult to suffer from stress.
The above manufacturing method, after the step of cutting, preferably includes the step of:
depositing metallic layers for electrodes to the second metallic layers exposed from a rear surface of the resin sealing body.
Since the metallic layers can be deposited to have a very small thickness by electrolytic or non-electrolytic plating as occasion demands, they are brought into intimate contact with the circuit board.
In the step of cutting of the resin sealing body, it is cut along a center line of each of the second metallic layers to provide metallic layers for external extension for adjacent semiconductor elements.
In this step, since the adjacent semiconductor devices can be mounted contiguously on the metallic substrate, the semiconductor elements can be densely arranged on the metallic substrate.
Preferably, the electrodeposition frame is resin sealed together with the semiconductor elements using the metallic substrate as a lower die. In this configuration, the metallic layers can be formed independently in the electrodeposition frame.
The above and other objects and features of this invention will be more apparent from the following description taken in conjunction with the accompanying drawings.